(the choicest or most essential or most vital part of some idea or experience; "the gist of the prosecutor's argument"; "the heart and soul of the Republican Party"; "the nub of the story")

2. inwardness

(preoccupation especially with one's attitudes and ethical or ideological values; "the sensitiveness of James's characters, their seeming inwardness"; "inwardness is what an Englishman quite simply has, painlessly, as a birthright")

3. inwardness

(the quality or state of being inward or internal; "the inwardness of the body's organs")